I don't know for ultracoin but this is what was tested for Yacoin when it was cpu only. You can see hashrate is roughly halved with each N increase as long as it doesn't change of memory type. For example, the change 13->14 shows a big loss because dataset doesn't fit in L2 cache anymore.

I see there are some questions that keep popping up again and again.  Might as well pop in to see if I can help in some way. 



N = 14  07 / 12 / 14 @ 04:20:16am UTC   At this N and beyond it will be more cost effective to mine with CPU.


Both CPU and GPU are affected similar, in terms of dropping hash rate each N increase.  However, the gap in actual hashrate gets smaller with higher N.  As well, CPU's actually "fall-off" slower in hash slightly than gpu / perform better later.
 For example 600khs GPU with N increase may be similar to; 600>290>130>60>25>10>5.
                 Comparing this to a CPU over same N increases; 125> 65>  35> 20> 10>5>2.5

Part of this reason was described best and quoted here;

"CPU's still have a number of advantages over GPU's and ASIC's.  They come with double precision floating point hardware, employ very advanced branch prediction mechanisms, incorporate at least 2MB of on chip L2/L3 cache, and are able to speculate through 4-6 branches even in ten year old machines.  GPU's can manage 2-5x better double precision floating point performance than a typical CPU, but in some benchmarks, they cannot even manage even speed.  The problem is worse for ASIC's, which must be custom designed around a specialized pipeline. "


Again quoting another location;  here is a representation of hash rate on a CPU vs increasing N values.



    Running 1500 scrypt hashes with N=2048 - 0.00109417 avg. sec per hash
    Running 1500 scrypt hashes with N=4096 - 0.00216536 avg. sec per hash
    Running 1500 scrypt hashes with N=8192 - 0.00450547 avg. sec per hash
    Running 1500 scrypt hashes with N=16384 -  0.00928228 avg. sec per hash
    Running 1500 scrypt hashes with N=32768 -  0.01895874 avg. sec per hash
    Running 1500 scrypt hashes with N=65536 -  0.04028997 avg. sec per hash
    Running 1500 scrypt hashes with N=131072 -  0.08082690 avg. sec per hash


test written in python on an  i5-4250U CPU @ 1.30GHz,


In the end it's not that CPU's hash way faster than GPU's at high N's; specifically, it's that CPU's cost less Watts per Kh/s to mine at higher N's.

 Some examples of hash rates and setups with CPU's and GPUs @ N = 14;  can be seen here - http://yacoinwiki.tk/index.php/Mining_Hardware_Comparison

You can see, as an example here @ N14

2x E5645 Procesors    2x 80W --   1.53Kh/s    

7950 GPU                  (250w)    1.3-1.5 Kh/s

As shown above.  the Processors will give approximately the same Kh/s for 160w versus 250w of a 7950.


There are a few CPU miners.  One is listed on the Ultracoin forum too.  However, there is one specific miner that is best and most up to date.
 
-Manual N parameters for multiple coins
-X86 and 64bit formats
-Stratum pool capable
-Scrypt optimizations for Scrypt-Jane

https://github.com/thirtybird/cpuminer/releases/

This is the absolute best CPU miner out there currently.  I believe it has all the needs being asked for.



Even though I'm not actively posting here;  I still hate to not help if I can.

Thanks
Prot

UftrEhcPx5hTY4YJvSziPi13dfZT9nXSqw