(Note: each test uses 1000 iterations of abbreviate-file-name.)

Vanilla Emacs 29.0.50:
----------------------

Empty ‘directory-abbrev-alist’
Local | Elapsed time: 0.051336s (0.016125s in 1 GCs)
TRAMP | Elapsed time: 2.173621s (0.501653s in 38 GCs)

100 items in ‘directory-abbrev-alist’ (no matches)
Local | Elapsed time: 0.316021s (0.133531s in 10 GCs)
TRAMP | Elapsed time: 2.459212s (0.633373s in 48 GCs)

100 items in ‘directory-abbrev-alist’ (all matches)
Local | Elapsed time: 0.539636s (0.327637s in 25 GCs)
TRAMP | Elapsed time: 2.484629s (0.642597s in 49 GCs)

500 items in ‘directory-abbrev-alist’ (no matches)
Local | Elapsed time: 1.075650s (0.500043s in 38 GCs)
TRAMP | Elapsed time: 3.241414s (1.006143s in 76 GCs)

500 items in ‘directory-abbrev-alist’ (all matches)
Local | Elapsed time: 1.302201s (0.696249s in 53 GCs)
TRAMP | Elapsed time: 3.261984s (1.018098s in 77 GCs)


Remove caching (patches 1 and 2):
---------------------------------

Empty ‘directory-abbrev-alist’
Local | Elapsed time: 0.075684s (0.012997s in 1 GCs)
TRAMP | Elapsed time: 2.196654s (0.514075s in 39 GCs)

100 items in ‘directory-abbrev-alist’ (no matches)
Local | Elapsed time: 0.361488s (0.130064s in 10 GCs)
TRAMP | Elapsed time: 2.517825s (0.641286s in 49 GCs)

100 items in ‘directory-abbrev-alist’ (all matches)
Local | Elapsed time: 0.616476s (0.340155s in 26 GCs)
TRAMP | Elapsed time: 2.534926s (0.641485s in 49 GCs)

500 items in ‘directory-abbrev-alist’ (no matches)
Local | Elapsed time: 1.239399s (0.502237s in 38 GCs)
TRAMP | Elapsed time: 3.394109s (1.012237s in 77 GCs)

500 items in ‘directory-abbrev-alist’ (all matches)
Local | Elapsed time: 1.472967s (0.707569s in 54 GCs)
TRAMP | Elapsed time: 3.401517s (1.008865s in 77 GCs)



TRAMP support (patches 1-3):
----------------------------

Local | Elapsed time: 0.076620s (0.013434s in 1 GCs)
TRAMP | Elapsed time: 3.543266s (0.864729s in 64 GCs)

100 items in ‘directory-abbrev-alist’ (no matches)
Local | Elapsed time: 0.365402s (0.131290s in 10 GCs)
TRAMP | Elapsed time: 3.736696s (0.955474s in 73 GCs)

100 items in ‘directory-abbrev-alist’ (all matches)
Local | Elapsed time: 0.608122s (0.340677s in 26 GCs)
TRAMP | Elapsed time: 3.818867s (0.956361s in 73 GCs)

500 items in ‘directory-abbrev-alist’ (no matches)
Local | Elapsed time: 1.232221s (0.499099s in 38 GCs)
TRAMP | Elapsed time: 4.599799s (1.313629s in 100 GCs)

500 items in ‘directory-abbrev-alist’ (all matches)
Local | Elapsed time: 1.479609s (0.708903s in 54 GCs)
TRAMP | Elapsed time: 4.656963s (1.345125s in 101 GCs)