YES(?, b + c + 4)

Initial complexity problem:
1:	T:
		(1, 1)    f3(a, b, c, d) -> f1(0, b, c, d)
		(?, 1)    f1(a, b, c, d) -> f2(a, b, c, e) [ b >= c ]
		(?, 1)    f1(a, b, c, d) -> f2(1, b + 1, c, e) [ 0 >= a /\ b + 1 = c ]
		(?, 1)    f1(a, b, c, d) -> f1(0, b + 1, c - 1, d) [ c >= b + 1 /\ 0 >= a /\ c >= b + 2 ]
	start location:	f3
	leaf cost:	0

Repeatedly removing leaves of the complexity graph in problem 1 produces the following problem:
2:	T:
		(1, 1)    f3(a, b, c, d) -> f1(0, b, c, d)
		(?, 1)    f1(a, b, c, d) -> f1(0, b + 1, c - 1, d) [ c >= b + 1 /\ 0 >= a /\ c >= b + 2 ]
	start location:	f3
	leaf cost:	2

A polynomial rank function with
	Pol(f3) = -V_2 + V_3 - 1
	Pol(f1) = -V_2 + V_3 - 1
orients all transitions weakly and the transition
	f1(a, b, c, d) -> f1(0, b + 1, c - 1, d) [ c >= b + 1 /\ 0 >= a /\ c >= b + 2 ]
strictly and produces the following problem:
3:	T:
		(1, 1)            f3(a, b, c, d) -> f1(0, b, c, d)
		(b + c + 1, 1)    f1(a, b, c, d) -> f1(0, b + 1, c - 1, d) [ c >= b + 1 /\ 0 >= a /\ c >= b + 2 ]
	start location:	f3
	leaf cost:	2

Complexity upper bound b + c + 4

Time: 0.096 sec (SMT: 0.090 sec)