You "may" have an issue with phosphor lag, or you might except it for what it is and notice that it becomes less and less noticeable the more you watch and as the panel ages.
For me phosphor lag is nothing in comparison to ghosting, I specifically stopped using lcds because of the terrible ghosting on most of them.
I used a Panasonic plasma as a computer monitor for a month and hardly ever saw any imAge retention, it was a 2008 model though that already had 1000's of hours on it and all Plasmas should be broken in with mixed content and care for the first 100 hours.
There aren't a lot of 46" Plasmas around right now, I think your pretty much limited to the x3 s30 and st30 all of which are last years models (the st30 is the best followed by the s30 and then the x3).
If you move down to a 42 inch or the 46" x3 then you lose the 1080p resolution for the odd resolution of 1024x768 (companies stopped using 1366x768 or the very rare 1280x720 to cut costs and power draw)
If your set on 46" rather than 50" then you should try to track down the s30 or st30 I'm not entirely sure of the difference between the 2 but they are both highly rated displays.
Don't go back any further than 2011 for Panasonic Plasmas as they had issues with rapidly rising black levels.
You could also look into a 50" 2012 model like the u50, ut50, or st50
Or even a full 720p (1366x768) Samsung pn51d450 from last year on the cheap if you can find one, last year was when Samsung got serious about black level and contrast but this is an average display in most other areas. The d550 apparently has lighter black levels so if you go above a d450 or d490 for 1080p youd want at least a d6500.
Samsung's Plasmas this year seem a little pricey to me and a lot of last year models had issues with fluctuating brightness which may have had something to do with dynamic contrast (you can't disable dynamic contrast completely on Samsungs as far as I know). The do appear to be the best this year for Image retention though.
You shouldn't have any problems with a plasma as long as you have a light controlled room to put it in and vary your game content with video for the first 100 hours so you don't burn in a health bar