FYI: a table showing a rough-and-ready relationship between the shift setting and the number of digits in the primes tested (data taken from the publicly-accessible gapdata.sqlite3.zip SQLite3 database file here on mega.nz).

Shift	Primedigits
16	82
17	83
18	83
19	83
20	84
21	84
22	84
23	84
24	85
25	85
26	85
27	86
28	86
30	87
31	87
32	87
34	88
35	88
36	88
37	88
37	89
39	89
40	90
41	90
42	90
43	90
45	91
46	91
47	92
48	92
49	92
50	93
50	92
55	94
57	95
57	94
58	95
60	95
60	96
63	96
63	97
64	97
69	98
72	99
74	100
75	100
88	104
90	105
95	106
96	106
100	107
100	108
105	109
110	111
112	111
115	112
120	114
120	114
121	114
122	114
123	114
123	115
125	115
126	115
127	116
128	116
130	116
132	117
144	121
150	122
150	123
156	124
180	132
187	134
188	134
189	134
190	135
191	135
192	135
200	138
225	145
250	153
255	154
256	154
256	155
286	164
300	168
301	168
308	170
328	176
330	177
348	182
350	183
351	183
356	185
360	186
380	192
381	192
382	192
383	193
391	195
392	195
392	196
404	199
409	200
409	201
412	201
412	202
414	202
415	202
416	203
437	209
440	210
441	210
442	210
442	211
443	211
444	211
445	212
446	212
447	212
448	212
449	213
450	213
451	213
468	218
472	219
472	220
473	220
474	220
476	221
477	221
478	221
479	222
480	222
481	222
482	223
483	223
502	229
504	229
506	230
508	230
509	231
510	231
511	231
512	232
540	240
541	240
542	241
543	241
544	241
546	242
547	242
574	250
576	251
602	259
607	260
608	260
608	261
630	267
634	268
640	270
698	287
699	288
700	288
702	289
720	294
732	298
760	306
762	307
764	307
764	308
765	308
767	308
790	315
794	316
794	317
797	317
798	318
799	318
828	327
829	327
830	327
831	327
831	328
832	328
860	336
888	345
896	347
920	354
920	355
986	374
987	375
988	375
991	376
992	376
1010	381
1011	382
1012	382
1014	383
1017	383
1019	384
1020	384
1020	385
1021	385
1022	385
1023	385
1023	386
1024	386

(I've found that the higher the shift setting, the lower the hashrate, unsurprising).

Gapcoin maxes out (nominally) at a shift of 1024 (as set by Jonny Frey, to avoid DoS) with  max prime digit length of 386, around number 10000 of 95000 in a sorted list of primedigit lengths taken from the prime gaps list (where the extreme upper regions see prime digit lengths of 100,000-200,000).

However, the criterion is maximum known merit and gap size, not the number of digits in the prime and it's worth noting that the current record for the largest prime gap with best merit is still held by Gapcoin with a(n inferred, from "87-digit prime") shift of 30:


Cheers

Graham