I am in a larger room using C2s with a pair of JL fathom 110 subs. C1s with a sub are nowhere near the performance, but agree C1 with sub v C2 w/out could be close.
FWIW - I acutaly think the C2 is a great spot in the confidence line. C1 is great monitor but short on bass and C4 only is really good for very large rooms. the C2 gives me, at leat, monitor like accuracy with very nice bass. Adding the pair of JL's made it perform incredibly well.
For your size room, C1 with a sub will be the best.
FWIW - I acutaly think the C2 is a great spot in the confidence line. C1 is great monitor but short on bass and C4 only is really good for very large rooms. the C2 gives me, at leat, monitor like accuracy with very nice bass. Adding the pair of JL's made it perform incredibly well.
For your size room, C1 with a sub will be the best.