I've not used the white roo pads, but I have used the black SaxGourmet pads for a bari job and they were fantastic. Very quiet when they close compared to traditional pads. I don't know why - they just are. The leather is soft like a fine piece of furniture. There may be other pads out there that are just as good, but I'll never bother looking for them. The SaxGourmet pads are awesome. The roo pads are made of the same leather - just not dyed black, so I would imagine they perform similarly. Personally, the tought of white pads possibly changing to some other color over time (moisture, age) doesn't thrill me, so what I can say is I've gone black and I'll never go back...
The ideal way to measure for pads is to remove the keys, remove the pads, and measure from the inside of the pad cup with some calipers or very carefully with a mm scale ("ruler" to you non-engineers). You can also measure from the outside of the pad cup and subtract 2mm, but I've ended up with some pads being a bit small doing it that way. Believe it or not 1mm can make a significant difference in how the pad fits. Too loose or too tight can cause problems - not necessarily, but it can. You definitely don't want to be fitting a 32mm pad into a 31mm cup.
So like any project, measure twice, cut once - so to speak. Taking the extra time to measure it properly is well worth a quality finish.
A warning - email Curt (musicmedic) first and let him know what pad sizes you need. They may or may not be available as the SaxGourmet and roo pads are a premium product and he's picky about the leather that's used.
It is possible that giving Curt your serial number, he may be able to approximate a set of pads without you measuring each one, but there's no guarantee that it will work out perfectly. There's lots of variation with all older horns (even modern ones to some extent).
Good Luck. If you have other questions, feel free to email me.