Intresting other example supporting 'High Count' numbers - 'Call of the Lion' from Tales of Heresy mentions that late-Crusade 'the Legionís strength had increased by almost twenty thousand in the last few years' when referring to the Dark Angels, which certainly fits better with 100,000-man Legions than smaller ones.
Interestingly, it suggests that there may be variation in Chapter size between Legions as well - Astelan remarks to a fellow Chapter Commander that 'you command more than a thousand of the finest warriors in the galaxy, as do I' (emphesis mine). Not conclusive, of course - you could argue that techmarines, command squads or whatever are outside the company/chapter structure and thus total numnbers are slightly in excess of 1,000. Still, worth pointing out.
This post has been edited by The Red Sorcerer on Feb 2 2010, 11:56 AM