I believe the main thing determining upgrade percentages is WHERE & WHEN you fly.

I bought my Silver status a month back with the Amex MR transfer when I decided to switch from AA to Delta and decided to go for Gold before year end so have been putting my butt in the seat quite a bit lately.

In the past 3 weeks, I have flown 15 different segments and have had 100% UG success, flying on CRJ 900's, an MD 90, several 757's & a 330. Since these were travels strictly for status, I carefully planned WHERE & WHEN I would travel to increase my chances of UG's using Expert Flyer and also had help from the very nice ladies in the Skyclub when I had to change flights a few times this past weekend due to cancellations and such.

I will be gold after next weekend but can't up for a much better percentage than that....