With regards to number position, mr2 would carry a better value then 2mr.
Although the LLN position is generally better than NLL, I think that this particular example is debatable, because "2" is frequently used in names to represent "to" as in " to Mr" ("To Mister") wheras Mr2 is more ambiguous in meaning. But, I confess that I am biased in this regard because I happen to own the rights to 2Mr.com.
Less debatable, are names w/ a "4" in first position, where "4" = "for", including: 4Dr, 4MD, 4Rx, 4DN, 4OS, 4IQ, and 4NY, all names that I have regged in various tld's). IMO, .info works particularly well w/ names of this type.
Because number/letter combos aren't a natural for type-ins and are not commonly used in searches, the key to their usefulness is in their brandability. When people see 4Rx, what immediately comes to mind? Do they think "prescriptions? Does 4Rx read as a shortened version of "For Rx". Does this transfer over to an association w/ "For Prescriptions"? The name is certainly short, but is the meaning clear enough to attract attention and is it catchy enough to be memorable? IMO, in tthe case of 4Rx, the answer to these questions is an affirmative, "Yes!", and that is how I will be presenting the name to companies that are selling and/or promoting prescription drugs, online.
I am using this criterium, along w/ search term popularity and Google links to the letter abbrev, (ie OVT/WT and Google numbers for Rx, Dr etc), to come up w/ a simple system for evaluating and estimating the name's potential and in establishing a target price for the name.
Examples:
(> meaning "stronger than")
4Mr>2Mr>3Mr
Mr1>Mr2>1Mr
4Rx>4DN>DN4 etc
Not exactly scientific and alot of room for judgement calls, but, for a starting point, I'm finding this approach helpful.