Which lens should I keep?

[Brittanicus]

I started off with the E-500 two lens kit, then I got offered an E-400 brand new at an unbelievable price, so sold the E-500 with the brand new 14-42mm that came with the E-400, as my wife had already bought me this lens.
I have just bought an E-510 two lens kit so naturally will be selling on the 14-42mm lens that comes with it.
I have the 40-150mm 1:3.5-4.5 lens that I got with my E-500 but have now also got the 40-150mm 1:4.0-5.6 with the E-510.
So the question I am asking is, in your opinions which lens should I keep out of the two 40-150mm's.
The 1:3.5-4.5 is obviously that little bit faster, but according to Wrotniak the newer 1:4.0-5.6 is sharper and as I know smaller and lighter. I've always loved my 40-150mm 1:3.5-4.5 but could do with some advice as I've not used the later lens and if I am to sell it would like to sell it as new.

[Elmo]

Shoot some shots and find out which gives the best quality.

With only a few shots and some care no one will know the difference.

[Tiberius]

Agreed. Take some shots of the same subject with the same settings (same shutter speed and aperture) and see what the difference in quality is. If there's one lens that consistently perfgorms better, keep it and sell the other one.

[Brittanicus]

Thanks guys, I did exactly that and have made my decision.
I am keeping the 40-150mm 1:3.5-4.5 lens that I got with my E-500.
1/ It is that little bit faster and I really can not see any difference in picture quality between the two lenses.
2/ I just like the feel of it in my hands more, it's just that bit chunkier and I don't really have petite hands anyway.