Is anyone having performance issues with the games? I have to set it at the lowest resolution to get a smooth frame-rate. I really don't mind playing it that way but I just want to know the reason behind not getting a solid frame-rate on a very old game on a high resolution.
Any answers/comments will be appreciated.

Any performance issue that people are experiencing is solely from the computer's ability to run dosbox.
It is either caused by an improper configuration, or a computer too slow to handle running the game.
Certain rendering modes work better than others on different video cards, OpenGL is usually the safest bet.
GOG's GUI tool doesn't work for me, so I have to manually edit the config file.
Dosbox runs from the config file, so it has to be edited to work, one way or another.
Make sure it's set properly.
Turning off unnecessary features can also help performance, so look up a dosbox tweak guide and find what works best for you.
Dosbox is a virtual machine, so you can see performance increases from updates and cvs builds. Try a cvs build if it seems necessary, you don't have to use the one that came with the game.

Update your DOSBox to 0.74 which was just released, it gives a notable performance boost for Blood.

What would be the correct way to update DOSBox if we're using the Blood Launcher McTecman posted? I don't mean to sound ignorant, just wondering.

copy the new files over the old ones.

CURSES! Foiled again!
How ironic that Blood II runs blindingly fast at maxed out settings, but Blood 1 is a no go! x-D
Anyway thanks for your reply!