I haven't heard a Grado cart, but at $140 it seems outclassed by the other gear you have, which all looks very nice. Your current table and phono should be able to reveal the improvements of a higher-end cart; I'd put in more money there.
I know I wouldn't be satisfied with just an Ortofon 2M Red (@ $100) with downstream gear like that, and I mention Ortofon because I've heard many of their carts, and and enamored with the sound-quality/value ratio they provide (via the 2M/Kontrapunkt/Cadenza lines) at every point up to around $2K.
While not familiar with Grado's cartridges, I am familiar with much of their headphone line; while they have some great qualities, the experience hasn't left me very confident in the value proposition of their other products. Ortofon, on the other hand, strikes me as the cartridge sound/value analogue to Sennheiser headphones. I know that the Ortofon 2M series works well on the Pro-Ject arms; my dealer uses that combo.
Break-in aside (I had a Kontrapunkt c that sounded bloody *amazing* right out of the box), if I were you I'd be looking at the 2M Bronze or Black -- the latter of which would definitely benefit from subsequent table upgrades! And yes, a speed-box is a great idea and can only help, but I'd make a cart upgrade top priority.
