Function detection is a well-known problem in binary analysis. While previous research has primarily focused on Linux/ELF, Windows/PE binaries have been overlooked or only partially considered. This paper introduces FuncPEval, a new dataset for Windows x86 and x64 PE files, featuring Chromium and the Conti ransomware, along with ground truth data for 1,092,820 function starts. Utilizing FuncPEval, we evaluate five heuristics-based (Ghidra, IDA, Nucleus, rev.ng, SMDA) and three machine-learning-based (DeepDi, RNN, XDA) function start detection tools. Among the tested tools, IDA achieves the highest F1-score (98.44%) for Chromium x64, while DeepDi closely follows (97%) but stands out as the fastest by a significant margin. Working towards explainability, we examine the impact of padding between functions on the detection results. Our analysis shows that all tested tools, except rev.ng, are susceptible to randomized padding. The randomized padding significantly diminishes the effectiveness for the RNN, XDA, and Nucleus. Among the learning-based tools, DeepDi exhibits the least sensitivity and demonstrates overall the fastest performance, while Nucleus is the most adversely affected among non-learning-based tools. In addition, we improve the recurrent neural network (RNN) proposed by Shin et al. and enhance the XDA tool, increasing the F1-score by approximately 10%.