What tonearm will better mine?


I have been running a 12" Jelco SA750L with an upgraded Decca Super Gold on a Garrard 401 for a few years. I'm happy with the sound and happy with my pre, power and speakers. (Croft 25R, EICO HF35s, -good tubes, Quad 57).
I keep hearing that my tonearm is a weak link even though it sounds pretty awesome to me. What would it take to replace the Jelco and make a significant improvement? What should I expect to hear better? Would I have to drill the massive plinth? Thanks.
128x128noromance
I’ve had many Deccas over the years in various arms. I think "boazro1" has it right with the Graham arm. I’m sure they have an an arm wand that will have the correct weight for the cartridge. The arm, as I recall, has variable damping that can be a boon for Deccas. The SME V has this feature too and I have heard such a set up with a Decca that was magical. ( The dealer should make sure the cartridge - any cartridge -has the correct azimuth before selling it to you.) Also, I understand that the Deccas need to be loaded differently (Ohms) than conventional 47KOhms so you may want to get that correct before trying new tonearm cables. I always find I like to do upgrades incrementally it increases enjoyment over the long term.
I have used several series 9 Ikeda (of Fidelity Research fame) cartridges that are a "moving coil Decca" with wonderful results. Unfortunately, the new Ikeda company will no longer be offering them. However, their new tonearms are supposed to be an update of the (rare) FR -64 and I have no reason to doubt that.
Yes, the Super Gold needs to be loaded at around 22k ohms resistance with 220pF capacitance, which creates the optimal electronically damped circuit with the cartridge. Another arm worth looking into is the Well Tempered. And if your Super Gold doesn't have the Decapod installed on it noromance, it may be the best thing you can do for it. 
Thanks bdp24. I tried loading the Decca with 33k many years ago in an Ittok and liked it better at 47k. The Croft preamps seem to play well either way. Tempted to do the DeccaPod. What improvements have you experienced? 
@binkt Please tell us more about your experience with the Pete Riggle Woody. I just read up on that arm which I have not heard, and it has many amazing features that I haven't seen before like on the fly azimuth adjustment. (Not sure if I am brave enough to do that). 
I also believe there is a version of that arm made specifically for use with SPU carts. 
Anybody else hear or own these? At $1900 including multiple headshells and weights for low/med/high compliance carts, it looks like a good value proposition, at least on paper. Cheers,
Spencer
One tweak that I have found to be very worthwhile with my 750D has been the Ammonite Acoustics mounting collar, which eliminates the slight slop in the OEM collar and ensures correct positioning of the arm as it relates to azimuth. Very important with more exotic stylus profiles. 

I also recently changed out the stock Jelco headshell to a Yamamoto HS4 Carbon Fiber headshell. This was a real eye (or ear) opener: pretty substantial improvements across the board in information retreival, overall presentation and dynamics. A no brainer for about $100 U.S. on ebay.
I have to second the Ammonite Accoustics mounting collar.  The brilliant thing about these is that he makes them from ebony!  Expensive? maybe, but not in "Hi-Fi" terms.  The great thing about ebony is that it is used to make musical instruments, oboes, clarinets for example.  All materials have a resonance, but the resonance of ebony is benign.  Match that with a Yamamoto Ebony (or Mpingo) headshell and you will get a real benefit.  Also there is the 'Shuggie Collar' as a tweak to the Jelco.  They are sold by ammonite accoustics.  The only downside to the Jelco is that the grub screw on the mounting collar is not centered.  A bit like rolling a log but pushing it with your foot at one end instead of the centre - it might go off course.  So great care is required in set up.  The aftermarket collar is is essential in mounting the arm to a Technics and I guess the same can be said for a Garrard.  The last tweak is silver rewiring.  I am not really a 'cable guy' but I do believe the smaller the signal the more important it is to have good a good cable.

As you may have guessed I am a Jelco owner.  If I was building another TT I would not go for a VPI or 'modern' tonearm.  I might even plonk another Jelco on it.  My other thought would be an SME M2-12.