Buzz,

Let me add this. I'm in the same position as you, I started learning on an Alpha 40 in April and moved up to the H9 Pulse XT 40 as my second plane. It makes for a great second plane, it flies like a 4* that everyone recommends so highly as a second plane, but I think it looks better. See for yourself:
[link=http://www.horizonhobby.com/Products/Default.aspx?ProdID=HAN4100]Pulse XT[/link]

I can attest that it makes for a great second plane. I too want to move into warbirds, but from all my reading here, warbirds can be delicate creatures and can be finicky in the air (higher stall speed, tip stalls, etc). For your second plane, and first low wing plane, you want something that is forgiving and allows you to adapt to the higher performance, not to mention getting use to a tail-wheel configuration. I know it's tempting to move into warbirds, but I would recommend getting good with aerobatics and greasing landings with a more forgiving plane first.