2 lights vs 1 light

Using two totally different lamps to light up your tank will still be better than that single bulb.

Perhaps some time in the future you can build a little box with regular light bulb sockets, paint it white inside and whatever sleek outside, and use two or three spiral bulbs. More even lighting, cheaper to replace bulbs, and might look better too (depending on your handy-ness).

why not upgrade to a 8" shop clamp fixture while using the same bulb. should be sufficient for your 10g.

I don't have anywhere to clamp the lamp. :/
I was going to get an incandescent hood for the 10G but I already had these two lamps, so I just wanted to know if I could get 40ish PAR without having to spend extra.

Can anyone give me a guesstimation on how much PAR the substrate is getting?

I don't remember seeing any measurements of the light from either of those lights or bulbs. You could guess how much PAR you now have about as well as I can.

Okay, I'll just try it out on the plants I want to grow.