here's some figures for you from my experiences...
LRP 3.5T brushless, uses approx 2700-2900mAh indoors on carpet (short track 80m) geared around 12.6 FDR whereas at 10.5 FDR outdoors on asphalt (long track 250m) pulls around 3900-4100mAh.
the IP3800 25C
packs I used initially didnt quite have the capacity (if it wasnt fully charged i might be 1 lap short of the 5mins) or the C rating to handle the LRP 3.5T brushless.. the packs heated up quite a lot and swelled slightly on their use, never vented or damaged the cells just swelled a little (90% sure this was the air expanding in the pack, not the cells)...
when i switched to the LRP 5300 28C packs (5.3*28=148.4A) i never had any heat issues with the packs and have always made the 5mins... this has ample overhead for the LRP 3.5T brushless - this would be much the same scenario with the IP5000 30C packs
to be honest, a 5.5T brushless and the IP3800 25C
packs would be adequate for most tracks but i would consider this the limit for these packs.. the IP3800 35C packs would have ample overhead for the 5.5T and probably be adequate for a 3.5T brushless also..
but as i've said i like to play it safe with C rating and capacity, especially when running low FDRs on low wind brushless motors
IP5000 30C sounds like to way to go to me