Probably minimal with either upgrade, unless you do a lot of photo or video editing, and then you have the problem of yours being a laptop.
Whether or not the upgrade has much of an impact really depends on what you use the computer for. Your average tasks of web browsing, email, word processing, etc, are not likely to see any real noticeable improvement. Same as if you upgraded to a new laptop. If you do more intensive work, like large spreadsheets, use any of Adobe's Creative Suite apps regularly, maybe if you're a developer... Those might see some benefit.
Also, having run into this at work, let me just state the following. I forget what the max CTO specs were for the Mid-09 MBP, but if you exceed those specs then that means Apple did not test the model in that configuration and the results may be unpredictable. Things may work beautifully, or they may crash and burn almost immediately, so be prepared for either possibility. At work someone with a Mid-2010 model tried installing their own drives, and they quickly started getting kernel panics. As soon as a drive meeting the CTO specs was installed, it stabilized, and if you went back over CTO specs, it would kernel panic again. OTOH, there are plenty of people out there who manage to do these kinds of upgrades without issue, but the point to stress here is that it's an UNTESTED CONFIGURATION: RESULTS MAY VARY.
I have a mid-2009 Macbook Pro 13", 2.26 GHz Inner Core 2 Duo. On purchase, I immediately upgraded the RAM to 4 gb (2x2GB DDR3 1067 MHz). Summer 2010, I upgraded the hard drive to a 640gb 5400 RPM (Western Digital Scorpio Blue).

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