different GPUs behind one mining proxy?

[calandro]

Hi,
is it possible with very different GPU hash speeds to work behind a mining proxy? For example I have a 7850 and two old 4850 in three PC. 7850 digs LTC with ~400khs, each 4850 with~100khs. Now I can put all three PC behind a local mining proxy and "add" the power or I create three different workers at the pool and each PC digs as a solo miner. What's the best choice? Does the fast card is braked with a proxy rather than by the slow cards? Is there a balanced ratio in total if I use a proxy? What's about the numbers of rejected shares with such different of speed?

Regards