Ever consider just getting 4 instead? It's nearly the same experience, really.
The problem with #5 is that even if you buy it, you didnt buy it. They took literally half of the roster and made it into expensive DLC. The rest of the game was also released in an incomplete state, because Capcom. For all I know, it may STILL be missing modes. I can tell you, the fanbase was NOT happy about this. Hell, it's still sitting at a "mixed" review on Steam. Right around 50%. You have to screw up MASSIVELY to get that low on Steam. That's not just bad... that's atrocious (and yes, it's the exact same as the console versions. Console players havent been any happier about 5, either).
Also... Really, it's a fighting game. New versions are very.... incremental. Often developers will make a "new" version... note the quotes there... and there'll be like, 2 new characters, but they'll want $60 anyway. In one notable occaision, there was ONE new character. Just one. Hardly any other improvements. Still wanted full price. I dont remember exactly which game THAT was but I do remember not being one bit pleased with it.
In THIS case, even PREVIOUS characters get locked into DLC (which I've never seen happen before), because Capcom fully knows they can and will get away with it. Or so they think. Again, "fans not happy" is a massive understatement.
But even without the DLC issue, in damn near all cases, new versions are NOT worth the money unless you're planning on taking it very seriously (as in, putting in hundreds of hours into practicing). Unless it's been like, MANY versions since you last bought an entry. But going from SF4 to SF5? Nah. Just buy the most recent version of 4.
Note that this is coming from someone with THOUSANDS of hours in many different fighting games.