>> Sonnet Encore/ST G4 1.8 GHz (SG4-1800, SG4-1800L) use slightly
>> overclocked MPC7447A (or more likely MPC7447B/C).

> According this page Sonnet Encore 1.8 GHz used also 7457

Thanks for the reference, but I believe it to be incorrect. Up to 1.4 GHz is definitely 7457 yes, maybe even 1.6 GHz is (doubtful), but 1.7 and 1.8 GHz are definitely later CPUs (7447A/B/C or maybe even 7448). I doubt they sold 42% overclocked CPUs.
See there for another reference that even says it has 7448: https://beta.ivc.no/wiki/index.php/PowerMac_G4_Upgrades#Upgrade_candidates

There're also some hints in the original Sonnet press releases for the 1.7 and 1.8 GHz versions in 12/2004 and 08/2005, respectively:

"These cards are based on the latest and fastest PowerPC G4 processor (used in Apple’s current PowerBook line) [...], and feature 512K of on-chip L2 cache."
http://web.archive.org/web/20060821124418/http://www.sonnettech.com/news/press/pr2004/pr120704_sg4_prcdrop.html

"These cards, based on the latest and fastest PowerPC G4 processor (used in Apple’s current PowerBook line) [...] feature 512K of SRAM on-chip L2 cache"
http://web.archive.org/web/20061111032204/http://www.sonnettech.com/news/press/pr2005/pr080105_prcdrp.html

Apple switched their PowerBooks from 7447 to 7447A in 04/2004 and to 7447B in 01/2005, so this cleary hints at those G4 iterations being used by Sonnet in their 1.7 GHz upgrade in 12/2004 and their 1.8 GHz upgrade in 08/2005.

I have a hunch that the SG4-1800 came with 7447B and the SG4-1800L with 7448, but I have no proof on that. It would explain why for the 1.8 GHz model, the official source hints at the 7447B but another source mentions the 7448.

> in manual from Kronos link is L3 cache visible ( but there lower freq ).

Yes, I don't expect them to have changed the product pictures in the instruction manuals for later L3-cache-less versions just because the chip arrangement on the PCB is different, as it has no bearing on the installation process.

> If Kronos has 7457 or 7447 can be easily checked by L3 presence
> (7457 has, 7447 hasn't).

745x processors can be deployed without connecting actual L3 cache to the corresponding pins. The PCB doesn't even have to have any footprint for L3 cache chip. In this case, any 745x CPU acts exactly like the corresponding 744x CPU. But I'm with you that in the case of the Sonnet Encore/ST G4 cards, 745x comes with L3 cache deployed.