Go with the 6,500, no question about that.
You are obviously trying to go the cheap route. But that's not always possible in this hobby, hehe.
These 19 watt bulbs emit a lot of heat. Your (I assume plastic) hood is very likely to melt. It has happened to a member of our club, and she was using the 13 watt bulbs.
Another problem may be that the hood can't accomodate the 19 watt bulb - it's diameter may simply be too big.
Just a week ago I made a hood for an 18T tank. I used galvanized tin - 90 degree angled pieces (used for roofing I believe) and porcelain sockets. Two 19 watt spiral bulbs + two 13 watt spiral bulbs make the hood hot but not smoking hot. I think that plastic would indeed melt - I can hold my hand on the hood for no more than 3-4 seconds
.
So if you insist on the spiral bulbs either find/make another hood or carefully try and see for yourself if your existing one will work.
I'd say that a better alternative to using the spiral bulbs is to use 2 or 3 normal output 18 inch fluorescent tubes (each one is 15 watts). The hardware to rig 3 of them should not exceed more than $30, but the bulbs themselves may be more expensive if you choose Coralife 10,000K ($20-30 each). Home Depot sells 18", 15 watt bulb that is meant for growing plants (5,000K if I'm not mistaken) for about $8. There are 2 or 3 such bulbs that HD sells, but check different HD locations because their stock differs. You may be able to end up paying about $50 for bulbs, ballasts, and end caps.
--Nikolay
