We used to have similar problem for every year till last year. the problem is you Transformers are almost dead. they donot provide the proper voltage.. we used to have 130-140V lowest often too.. routine used to be 160-170V. the problem of overload is much less impact than the problem of dying transformers.. if your town or street people offer to buy a new transformer with money collection all of you will receive benefit for many years.. take care of the transformer though,. it get stolen sometimes. its very expensive... even in highest loads it would remain above 180V for all the street.. and routine would be 230-240V..
as for efficiency, almost all stabilizers are to provide efficient stabilization upto 180V. going below puts lots of stress on stabilizer and too much heat.. like fry an egg hot. eventually they will burn unless it is 2x the capacity of load..
simply consider like half of the extra capacity is used in converting load from 170V to 220v.. go below and you would need as much extra capacity to manage that with ease,.
if you have a triple phase meter, i would suggest diving load equally in 2 phases or put oven or ac on the one with higher voltage. and then split load between 2x 7500W or 2x 10KW stabilizers... 2 smaller stabilzers are always going to be better than one large one.
if single phase, still better to split load between 2x stabilizers.. since you wont be using every single appliance all the time, neither of these would be overloaded and ensure higher volts at much less heat.
you must ensure the winding is pure copper.. winding is important to be copper.. wiring can be silver/aluminium, but core must be copper.
in local, general and universal are comparatively better brands if you can find them yourself official shops in hall road.
some people have good reports from Rimco too, gujranwala based. and cheaper if you order to them directly.
Japanese stabilizers new can be searched on Brandereth Road lahore. but difficult to find. and extremely expensive.
in local, Aetco are the supposedly top brand in Servo motor stabilizers.. their prices are very high, but come with warranty and are suposed to be best.. other close mentions are Inverex and i guess anything on Metro.
imported stabilizers can be bought from importers in used lots at cheaper rates and very high industrial grade standards but are used and repairs can be difficult since no spare parts..
there is a new trend to persuade / Fool people towards Digital stabilizers. since i have no idea about those which are available in market, ijaz wuld be able to shed proper light on them. in theory, Digital stabilizer should be a Step less voltage maintenance with 95+ % efficiency and minimal electronic kit to worry about and much less heat with silent operations..what is available in market is i dont know.