Help with my Pyro/Knight Build

Hi!

I bought Dark Souls one week ago and I think it's really a great game...way better than Demon's Souls!

However, I decided to build my character using these guidelines:
http://darksoulswiki.wikispaces.com/Pyro-Knight-Build

Now I'm level 37 and my stats are:
Vitality 20
Attunement 18
Endurance 20
Strenght 16
Dexterity 12
Resistance 12
Intelligence 10
Faith 12

My next challenge will be Sen's Fortress and I'm not sure that my Drake Sword will be really useful in there...
My question is simple:
Is it worth to upgrade Drake Sword, or should I find another weapon? What kind of weapon is a good choice with a build like the one I linked above?

Thanx

i its not worth it to upgrade the drakesword what i do is use a weapon with bleed (i use a katana) and go through sen cuz their weak to bleed (i think) and eventually you will find a mimic which will drop the lightning spear and you can use that.

With those stats I'd suggest getting the Claymore off the Drake bridge and upgrading it to +10, ready for lightning ascension in Anor Londo. About 1/3 through Sen's Fortress you will come across the Lightning Spear, which you should be able to wield effectively until you can begin upgrading your own weaponry.

Do not upgrade the Drake Sword, it uses precious Dragon Scales which can be put to much better use later on.

You just need combustion to go through Sen, well untill the boss. Let the lizards hit your shield and, when they stagger, put them on fire. Your combustion will make a critical. If your pyro glove is around +10 you will kill them with 2/3 combustions. It is fairly easy. If you have buy the two spells, 32 cast will make you to the bonefire.

You will be able to wait for your weapon.

Thanx guys!
I really appreciate your help!

I'll try to use Combustion until Lightning Spear. Meanwhile I'll start the upgrade of the Claymore!