When I was searching out cams I looked at the A310 and If I remember correctly the 310 has the newest chip from Fuji that "supposedly" increases the useful pixel resolution due to a change in pixel shape. Theoretically, from Fuji, it gives a better resolution matching a 5 or 6 mp camera. Maybe I'm exaggerating But the essence is there. I haven't seen anyone mention it in a review tho.
I have no experience hands on with the 310. It is slightly smaller than the 210
210 = 3.9x2.6x2.1 inch 7.9 oz
310 = 3.8x2.5x1.3 inch 6.7 oz
A consideration is the way it fits your hand. I thought the 310 would be slightly small for my mitts.
Tom