The log information via xtool when repacking FH5:
Code:
Duplicates: 409792 (8.55 GB) [13.1 GB >> 22.2 GB]
Srep decompression memory: 5.30 GB [19.9 GB*]
Something you have to keep in mind when repacking Forza Horizon 5 is that this game has a lot of duplicates because its also a big game. If you use srep, it will request
20 GB for decompression memory or (
5 GB if you used -dd while xtool itself will request
8.5 GB, about 13 GB overall, ~7 GB memory savings) and since you made a post that you wanted to control srep's a# parameter, I can only assume that when you ran decompression before, you had more system memory available than when you ran it this time.
The speed reductions seems to be related to you not having enough memory to install the game without srep or xtool making virtual temp files which incur speed penalty.
Games like these are the reason I added GPU memory feature in xtool because it would offload some memory onto the GPU which typically isn't used when installing games (if you have 8GB GPU, xtool would require 1GB instead of 8.5 GB, while 7.5GB will be on the GPU then installation would need 6GB instead of 20 GB which srep initially required), though not ready because it's not thoroughly tested on a lot of systems to see if it works without issues. 
I ran a test between 0.7.4 against older releases, they all produce the same results and have the same speeds when decoding (at least within margin of error) and 0.7.0+ encodes faster. Decoding speed in 0.7.4 is slightly slower but reasonable because of memory usage optimisations that were made in 0.7.2, all versions used 220 MB+ for decoding while 0.7.4 used 73 MB.
ForzaHorizon5\DLC\MicrosoftExpansion2FH5\media\Tra cks\Falcon\bin.zip
Code:
0.7.4
Compressed 1 file, 1,893,356,830 => 2,847,735,336 bytes. Ratio 150.41%
Compression time: cpu 1.36 sec/real 20.95 sec = 6%. Speed 90.39 mB/s
Tested 1 file, 2,847,735,336 => 1,893,356,830 bytes. Ratio 150.41%
Testing time: cpu 0.19 sec/real 22.40 sec = 1%. Speed 84.52 mB/s
0.7.0
Compressed 1 file, 1,893,356,830 => 2,847,735,336 bytes. Ratio 150.41%
Compression time: cpu 1.41 sec/real 20.57 sec = 7%. Speed 92.05 mB/s
Tested 1 file, 2,847,735,336 => 1,893,356,830 bytes. Ratio 150.41%
Testing time: cpu 0.33 sec/real 22.06 sec = 1%. Speed 85.84 mB/s
0.6.9
Compressed 1 file, 1,893,356,830 => 2,847,735,092 bytes. Ratio 150.41%
Compression time: cpu 1.48 sec/real 25.08 sec = 6%. Speed 75.50 mB/s
Tested 1 file, 2,847,735,092 => 1,893,356,830 bytes. Ratio 150.41%
Testing time: cpu 0.14 sec/real 21.56 sec = 1%. Speed 87.81 mB/s
0.6.5
Compressed 1 file, 1,893,356,830 => 2,847,735,092 bytes. Ratio 150.41%
Compression time: cpu 1.38 sec/real 24.58 sec = 6%. Speed 77.03 mB/s
Tested 1 file, 2,847,735,092 => 1,893,356,830 bytes. Ratio 150.41%
Testing time: cpu 0.30 sec/real 22.06 sec = 1%. Speed 85.83 mB/s
0.5.3
Compressed 1 file, 1,893,356,830 => 2,847,735,104 bytes. Ratio 150.41%
Compression time: cpu 1.39 sec/real 25.08 sec = 6%. Speed 75.51 mB/s
Tested 1 file, 2,847,735,104 => 1,893,356,830 bytes. Ratio 150.41%
Testing time: cpu 0.16 sec/real 21.56 sec = 1%. Speed 87.81 mB/s
0.4.0
Compressed 1 file, 1,893,356,830 => 2,847,735,104 bytes. Ratio 150.41%
Compression time: cpu 1.38 sec/real 24.39 sec = 6%. Speed 77.64 mB/s
Tested 1 file, 2,847,735,104 => 1,893,356,830 bytes. Ratio 150.41%
Testing time: cpu 0.41 sec/real 21.56 sec = 2%. Speed 87.82 mB/s