Just think "small is beautiful". I'm on a 26Kbps dial-up line out in the boonies so something like 800x600 is ideal. You can send something larger and I'll shrink it down using Paint, or you can shrink it first, up to you.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8