Don't worry. For anything rendering related that CPU will be quite good!
Viewport, certain Photoshop tasks, simulating and stuff like that which predominantly scales with multiples CPU cores badly (i.e only uses 1-2... cores) will however be slower. In fact, they could be significantly slower but that might not mean much to you because even if a PS filter is being applied 50% slower, your render times are going to be like 3/4 faster. So if your filter takes 2 minutes to apply instead of 1 minute you might be fine with it if your render renders for 2 hours instead of 10 :)
So its a bit of a trade-off. Generally people stick to higher clocked CPUs for workstation and put it high core - low clock Xeons in the role of render nodes.
That said, if you buy something like a 2690 you are going to have a high core count and also higher than your usual Xeon single core clocks. The 4790k, 6700k and 7700k (and Xeons versions E1xxx) are pretty much the fastest 1-4 core CPUs you can get - simply awesome for single threaded stuff.
Like I said though, are you going to notice it that badly? Probably not. Depending on your work and what you do you might be just fine (and rendering including IR is going to be WAY faster) :)
Hope it helps!
