A thing to take note is, with greater XP reward should come greater GP reward, so a lvl7 player doesn't finish with the equipement of a 4th level character, but that, I think, will be handle correctly.
Rinaldo has been running since the start and is now 4th level (2nd character to reach it I think). Which mean we can hope to have our first 7th level not before another year, and the first EPIC before... maybe 5 or 6 year (wonder if anyone will reach that level...). Anyway, the big disadvantage to slow progress is the slow development of the world (well, maybe it is an advantage...). Coming back to Rinaldo, he is a merchant, and I hope to open a shop with him, but it won't be before he reach a few level in Trader PrC (so, maybe around 7th), so it would be another thing to think about.
Personally, I am fine with the 50xp/month/level, but I would suggest a slower rate at higher level, as I've always favored world with few high level, and I don't want to see a bunch of 15th level ruling the world and starting to ruin the interest of the low-level characters (which frequently happen in mass computer game).