The 5000 year thing is a myth. The Cholas invaded half of South East Asia.
Gupta empire went all the way to Iran
slight correction- guptas borders in the west are ambiguous. Parts of Sindh definitely belonged to Sassanians, as we have shit tons of Sindhi-Sassanian coins from this period in Sindh and no local coinage, indicating imperial sassanid mints controlled trade in parts of Sindh (mostly west bank of Indus).
Gupta control directly went into skardu, gilgit region- we have rock carvings of that, which means peshawar region MUST also be under Gupta direct control, else you cannot get into skardu-gilgit area from India without controlling the north Indus watershed.
Now how far into Afghanistan Gupta empire extended, is subject to question :from foundation of Sassanian empire in 230s CE to about 360s, the area was under a junior sassnid line, called kushanshahs. Then that line ended/got revoked by senior line and these turkic people called Chionites in roman sources and kidarites in Iranic sources took over and they did what steppe nomadic tribes pouring into balkh region always do - fight for a while with Iran and become its vassals, except for a period the Kidarites also were Gupta vassals- but if it happened before or AFTER they crossed into gandhara half a century later (in 400s) and settled under pressure from the Yeopthal huns ( Abdalis, aka the Hepthalites) is unknown.
What we do know, is the extent of Sassanian Imperial power at its lowest ebb in the east, for period of 300-500 CE, the period of gupta empire's rise, dominance and decline to near end : Balochistan & Entire Balochistan region + parts/all of Sindh, everything in Sistan basin west of Kandahar and everything west of the Maryy oasis + herat line = Sassanian.
The few times this eastern front changed, is under pressure from Turks such as Chionites, Hepthalites, Alkhan huns etc pouring in and facking over iran, but this region - the region of Kandahar west-wards has consistently been either iranic or central Asian irano-turkic for ALL of this period. Gupta empire, therefore, at its maximal extent in the west, either conquered or vassalized Sindh +Kabul valley where the chionites lived.
